Slug riveting method and apparatus

ABSTRACT

RIVERTING APPARATUS HAVING UPPER AND LOWER ANNULAR CLAMPS ENGAGING THE WORK PIECES AND COAXIAL UPPER AND LOWER HEAD FORMING ANVILS POSITIONED TO HOLD A CYLINDRICAL RIVET BLANK OR SLUG IN THE RIVET HOLE IN THE WORK SHEETS WITH BOTH ENDS OF THE BLANK PROTRUDING FROM THE WORK PREDETERMINED DISTANCES TO PROVIDE HEAD FORMING MATERIAL. IN FORMING THE HEADS THE UPPER ANVIL IS FIXED AND THE LOWER ANVIL IS MOVED AGAINST THE BLANK TO SQUEEZE-FORM A HEAD. INITIALLY THE FORCE OF THE UPPER CLAMP EXCEEDS THE SQUEEZE FORCE OF THE LOWER ANVIL BUT AFTER THE LOWER HEAD IS PARTIALLY FORMED THE INCREASING FORCE OF THE LOWER ANVIL OVERCOMES THE FORCE OF THE UPPER CLAMP AND CONTINUED SQUEEZEING MOVEMENT OF THE LOWER ANVIL MOVES THE WORK PIECES AND THE RIVET BLANK UPWARDLY TO SQUEEZE-FORM THE UPPER HEAD AGAINST THE STATIONARY UPPER ANVIL AND COMPLETES THE FORMATION OF THE LOWER HEAD.

Jan. 26, 19.71 T. H. SPELLER 3,557,442

' SLUG RIVETING METHOD AND APPARATUS Filed April: 2; 1968 2 Sheets-Sheet 1 FscaQl.

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\"IiNT'UR. THOMAS H. SDELLER BY ATTODNEYS \\\\\\K\\\\\ Ill/Idll/IIIA l ZI Jan. 26, 1971 T. H. SPELLER SLUG RIVETING METHOD AND APPARATUS 2 Sheets-Sheet 3 Filed April 2, 1968 ATTORNEYS United States Patent 3,557,442 SLUG RIVETING METHOD AND APPARATUS Thomas H. Speller, Buffalo, N.Y., assignor to General- Electro Mechanical Corporation, Buffalo, N.Y. Filed Apr. 2, 1968, Ser. No. 718,096 Int. Cl. B21j 15/22, 15/12; B23p 19/04 U.S. Cl. 29-526 Claims ABSTRACT OF THE DISCLOSURE Riveting apparatus having upper and lower annular clamps engaging the work pieces and coaxial upper and lower head forming anvils positioned to hold a cylindrical rivet blank or slug in the rivet hole in the work sheets with both ends of the blank protruding from the work predetermined distances to provide head forming material. In forming the heads the upper anvil is fixed and the lower anvil is moved against the blank to squeeze-form a head. Initially the force of the upper clamp exceeds the squeeze force of the lower anvil but after the lower head is partially formed the increasing force of the lower anvil overcomes the force of the upper clamp and continued squeezing movement of the lower anvil moves the work pieces and the rivet blank upwardly to squeeze-form the upper head against the stationary upper anvil and completes the formation of the lower head.

BACKGROUND OF THE INVENTION This invention relates to forming of rivet heads and particularly to slug riveting wherein a cylindrical rivet blank is inserted in a rivet hole in the work and heads are then formed at both ends of the blank to complete the rivet joint.

In conventional slug riveting, heads are most commonly formed by impact tools which strike the ends of the rivet blank to form heads thereat. Due to many objections in impact riveting attempts have been made to form rivet heads by exerting static pressure forces against the ends of the rivet blank to form the heads, such riveting being referred to as squeeze riveting.

In forming the rivet heads with the rivet blank in position in the work the riveting force tends to bulge the shank portion of the rivet in the rivet hole which takes up part of the clearance between the rivet shank and the rivet hole. This bulging of the shank is desirable, particularly if properly controlled. However, in impact riveting, due probably to inertia forces, the bulging of the rivet shank is more or less concentrated adjacent to the ends of the shank adjacent to the rivet heads, thus producing a distinct hourglass form of shank. In squeeze riveting as heretofore known the bulging of the rivet shank is improved but still produces a lesser hourglass form of shank.

In impact riveting control of the position of the rivet itself in an axial direction is difficult to achieve, with the result that imperfect rivet heads are difficult to avoid. Here again, conventional squeeze riveting, wherein squeeze forces are applied to opposite ends of the rivet bank simultaneously or successively, improves the control of formation of the rivet heads but still leaves much to be desired in this particular. In this case also axial movement of the rivet blank results in unequal metal distribution at opposite ends and resultant imperfect head formation.

3,557,442 Patented Jan. 26, 1971 BRIEF SUMMARY OF THE INVENTION In proceeding in accordance with the principles of the present invention a rivet slug is inserted in the rivet holes in the work pieces with the work pieces clamped together at their opposite sides. A backup tool or anvil is positioned in abutment with one end of the rivet blank and a rivetforming anvil is squeezed against the opposite end of the blank to form a rivet head. During this initial formation of the first head of the rivet the clamping force from the side of the work pieces adjacent to the backup member exceeds the clamping force from the side of the work pieces adjacent to the head-forming anvil and also is of sufiicient magnitude to hold the work pieces against the head-forming forces applied to the one end of the rivet blank by the rivet-forming anvil.

After the first head is thus formed or is at least suflici'ently formed to prevent axial dislocation of the blank or slug, the force of the head-forming anvil overcomes the clamping force at the side of the work piece adjacent to the backup member so that the work pieces then move toward the backup member, which is held stationary throughout, and the backup member forms the second head.

As indicated above this mode of squeeze-forming rivet heads at the opposite ends of a rivet slug or blank by forming or partially forming a rivet head at one end of the blank, then causing the work to move toward a backup member at the other end of the blank to form the second head of the rivet, is a distinctly new approach since heretofore it was considered that proper control of the head formation in slug riveting could only be achieved by holding the work pieces in a fixed position between the rivet-forming tools.

In addition to affording better control of the position of the slug and accordingly more perfect head formations, the present novel method of squeeze-forming rivet heads is found to much further reduce the hourglass form of the rivet shanks, that is, it tends to produce a more uniform bulging of the rivet shank along its length, which is a highly desirable result.

Since the backup member employed in the method of the present invention, which also comprises the anvil for forming one of the heads of the rivet, is fixed and stationary at all times, and only the rivet-forming anvil at the opposite side of the work piece moves axially against the rivet blank, the' accuracy and control of the rivetforming operation is greatly enhanced. Furthermore, since the head's of both rivets are squeeze-formed by a single continuous movement of the rivet-forming anvil toward the backup member, the entire riveting mechanism is greatly simplified.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 through 5 are successive somewhat diagrammatic vertical cross-sectional views through one form o the work clamping and rivet forming tools of the present invention illustrating the several steps practiced in one form of the method of the present invention.

:FIG. 6 is a schematic vertical cross-sectional view of the lower clamping and rivet head forming mechanism of FIG. 1; and

FIG. 7 is a general hydraulic circuit diagram illustrating the sequential operational steps of the rivet-forming and work-clamping mechanism.

DESCRIPTION OF THE PREFERRED EMBODIMENT Reference will first be had to FIGS. 1 through and the several rivet forming steps of the present invention will be functionally described. In FIGS. 1 through 5 a pair of work sheets 10 and 11 have a rivet receiving hole 13 formed therethrough including a countersink 14 at one end thereof. It is to be understood that the work clamping and rivet forming mechanism of the present invention may comprise elements of a riveting machine which includes drilling or other mechanism for forming and countersinking the rivet holes. Since the rivet hole forming mechanism and the rivet blank feeding and inserting mechanism are conventional and form no part of the present invention the details of these mechanisms need not be illustrated herein.

Referring to FIG. 1, the numeral 15 designates a lower rivet head forming anvil which is vertically movable in a lower work sheet clamping sleeve 16. The upper work clamping sleeve is designated 17 and the upper rivet head forming anvil is designated 18 in FIG. 2, this element being withdrawn and accordingly not illustrated in FIG. 1.

Proceeding with the functional description of the foregoing tools or implements, the work sheets 10 and 11 are securely clamped between the lower and upper clamping sleeves 16 and 17 and at this point a generally cylindrical rivet slug or blank is inserted in opening 13 with the lower and upper riveting head forming anvils 15 and 18 moved to the positions shown in FIG. 2 to properly locate and hold the slug 20 axially to provide the proper head forming protrusions at the lower and upper sides of the work pieces 10 and 11.

At this time the head forming operation commences and the lower head forming anvil 15 moves upwardly against the lower end of slug 20 to begin the lower head forming operation and at this time the upper head forming anvil 18 is hydraulically locked or securely held in the position illustrated in FIGS. 2 and 3. At this time the clamping force of the upper clamping member 17 exceeds the clamping force of the lower clamping member 16 and is of such magnitude as to permit the lower anvil member 15 to move upwardly and at least partially form a head 21 at the lower end of the rivet blank or slug 20, as shown in FIG. 3, without upward movement of the work sheets 10 and 11.

As the formation of the lower head 21 proceeds beyond the stage illustrated in FIG. 3 the upward force of lower head forming anvil 15 exceeds the clamping force of upper clamp member 17, the upper head forming anvil 18 being still hydraulically held against axial movement. Accordingly, the upper clamp member 17 yields in an upward direction whereupon the continued upward movement of lower head forming anvil 15 simultaneously forms an upper head 22 and completes the formation of lower head 21, during which head forming the work sheets 10 and 11 move upwardly toward fixed upper anvil 18 due to the upward yielding of upper clamp member 17 to the predominant squeeze force of lower anvil 15.

This upward movement of the work sheets 10 and 11 will automatically adjust itself in magnitude to the inherent axial shortening of the upper protrusion of the rivet slug in response to the formation of the upper head 22. FIG. 5 merely illustrates the withdrawn or released positions of the lower and upper clamp members 16 and 17 which permits removal of or shifting of the work sheets 10 and 11.

FIG. 6 shows schematically the pressure cylinder arrangement at the lower side of the clamping and riveting structure which provides clamping force for lower clamp 16 and rivet-forming pressure for lower anvil 15. In effect, lower head forming anvil 15 is fixed to a piston 23 in a hydraulic cylinder 24 and clamp member 16 extends about anvil 15, the latter having an annular enlargement 25 which acts as a piston within the annular lower clamp member 16. A coil spring 26 normally urges the clamp member upwardly with respect to lower anvil 15 to the approximate position illustrated in FIG. 6.

The coil Spring 26 tends to maintain clamping member 16 in a raised position relative to lower anvil 15 initially. Air pressure is introduced into the space between anvil 15 and clamp member 16 which houses spring 26 and establishes a base or initial pressure within this space.

When operating hydraulic pressure is introduced to the lower end of cylinder 24 piston 23 and the mechanism supported thereabove moves upwardly until clamp member 16 meets the lower side of the work and as piston 23 proceeds upwardly, the lower anvil 15 reaches the initial position illustrated in FIG. 1 and the further compression of the air within the space which houses spring 26 establishes an upward clamping force by clamp member 16 which is of approximately the same as or at least approaches the magnitude of the downward clamping force which is applied to upper clamp member 17.

Referring now to the hydraulic circuit diagram FIG. 7, the numeral 34 is applied to four hydraulic piston and cylinder mechanisms which operate jointly and are arranged circumferentia-lly to apply axial downward force to upper clamping member 17. One of the piston and cylinder mechanisms 34 is schematically illustrated in FIG. 1. In FIG. 7 a further piston and cylinder mechanism 35, hereinafter referred to as a bucking cylinder, is fixed t0 the upper end of upper head forming anvil 18.

A source of hydraulic fluid pressure for the clamp cylinders 34 and bucking cylinder 35 is shown at 36 and is connected by way of a four-way valve 37 and a pressure reducing valve 38 to the upper ends of the several clamp cylinders 34 by way of a conduit 39. A pressure limiting relief valve which discharges to a hydraulic reservoir is designated 40 in FIG. 7. With the four-way valve 37 connected as indicated the lower ends of the clamp cylinders 34 are connected to a reservoir 41 by way of a conduit 42. Thus the clamping force of the upper clamp members 17 is at a constant magnitude throughout the rivet forming cycle as established by reducing valve 38.

After the work is thus clamped a four-way valve is actuated to connect a relatively low fluid pressure line 51 to the upper end of cylinder 35 by way of a line 52 which moves upper anvil 18 down to a position established by a physical mechanical stop (not shown). This downward movement introduces the rivet slug or blank 20 by means of conventional rivet feeding mechanism and also brings upper anvil 18 down to the position illustrated in FIG. 2 wherein correct upper and lower protrusions of rivet blank 20 are established by the illustrated positioning of the lower anvil 15 and the upper anvil 18.

At this point, four-way valve 50 moves to a blocking position and a second four-way valve 54 is shifted to apply full hydraulic pressure to a pressure intensifying chamber 55 by reason of which intensified hydraulic pressure is applied through line 56 to the upper end of bucking cylinder 35 which effectively prevents upward movement of upper anvil 18.

When the upper ram reaches this stage in the sequence of operation all of the four-way valves which control the lower ram are closed and the lower anvil 15 is in the initial position shown in FIG. 2. At this point four-way valves 60 and 61 operate to apply fluid pressure to the lower end of cylinder 24 which is regulated as to magnitude by a relief valve 63 which has thus been connected to the operating line 64.

Lower anvil 15 raises and begins the squeeze deformation of the lower end of the slug 20 until the formation of the head reaches the degree illustrated in FIG. 3. At this point upward motion of lower anvil 15 continues and overcomes the bias force of upper clamp member 17. This same force is transmitted through the slug 20 to the hydraulically locked upper anvil 18, thus squeeze forming the upper head 22 and completing the formation of lower head 21.

After the formation of both rivet heads is completed, as illustrated in FIG. 4, four-way valve 60 reverses and fourway valve '61 shifts to connect the lower end of cylinder 24 to the reservoir. Thus the lower anvil 15 and lower clamp member 16 are moved to their lower retracted positions as illustrated in FIG. 5.

After the lower clamp and lower anvil are thus retracted four-way valve 50 of the upper ram hydraulic system shifts to connect the low pressure line 51 to the lower end of bucking cylinder 35 and connects line 52 to reservoir thus retracting the upper anvil 18. At this time four-way valve 37 reverses to connect the pressure source 36 to the lower ends of the cylinders 34 to raise the upper clamp members 17 to open position.

Proper sequencing of the operation of the several control valves for effecting the foregoing operations is by conventional limit switches which are operated when predetermined movements of the parts occur and pressure responsive switches which operate when predetermined pressure conditions are reached. Each of the limit switches and pressure switches triggers the subsequent stage of operation of the several four-way valves. The manner of positioning and connecting the necessary control switches is conventional and need not be described in further detail.

As in conventional riveting machines of this general class, rivet head shaving or milling tools may now move into operative position with respect to the upper rivet head 22 to shave or mill the material above the upper surface of upper work sheet 10 down to the surface of the work sheet.

In the embodiment described and illustrated, the upper rivet head forming anvil is described as being stationary at all times, and the other implements are described as moving upwardly relative thereto. The described movements of the parts may merely be reversed without departing from the principles of the present invention and without involving any difference in the relationship of the parts with respect to each other at any time during the riveting operation. This reversal to produce the same identical riveting action described above is achieved by holding the lower rivet head forming anvil '15 in a fixed position at all times and moving all of the other implements downwardly relative thereto. In this reverse procedure all of the parts at every stage of the operation will occupy identical positions relative to the other parts, and these relative positions would be accurately illustrated by FIGS. 1 through of the drawings herein, whether the upper anvil 18 is the stationary member, as in the specific embodiment described above, or whether the lower anvil 15 is the stationary member and the other parts move toward the same.

I claim:

1. Apparatus for forming heads at the opposite ends of a rivet blank with the blank positioned in a rivet hole extending through work to be riveted, said apparatus comprising a pair of clamp members adapted to move toward each other to clamp the work therebetween, means for inserting a rivet blank in said rivet hole with the work thus clamped, a bucking tool and means for moving the same against one end of said rivet blank and for retaining the same in a fixed position relative to and in abutment with said one end of the rivet blank, a rivet head forming tool having an initial position in abutment with the other end of the rivet blank whereby the blank is positioned axially to protrude a controlled distance at each side of the work for proper head formation, means for moving said rivet head forming tool and said bucking tool relatively toward each other, means for holding the clamp member at the bucking tool side against the work with a force greater than the force required for the rivet head forming tool to at least partially form a rivet head but substantially less than the full squeezing force of said head forming tool whereby relative squeezing movement of said tool against said rivet blank first at least partially forms the rivet head at the end of said blank engaged by said rivet head forming tool then by continued relative movement of said head forming tool and said bucking tool toward each other overcomes said clamp member force and moves the work, the clamp members, and said blank relatively toward said bucking tool to squeeze form a second head at the bucking tool end of the blank and complete the first rivet head formation.

2. Apparatus according to claim 1 wherein the clamp members are annular and coaxial with said bucking tool and said head forming tool.

3. Apparatus according to claim 1 wherein the squeezing movement of said tool against said rivet blank is continuous and progressively increasing until both rivet head formations are completed.

4. Apparatus according to claim 2 wherein the squeezing movement of said tool against said rivet blank is continuous and progressively increasing until both rivet head formations are completed.

5. Apparatus according to claim 1 wherein said clamping member holding means and said rivet head forming tool moving means comprise fluid pressure force means.

6. Apparatus according to claim 5 wherein the squeezing movement of said tool against said rivet blank is continuous and progressively increasing until both rivet head formations are completed.

7. A method of forming heads at the opposite ends of a rivet blank with the rivet blank positioned in a rivet hole extending through the work to be riveted which comprises clamping the work between a pair of clamp members, inserting a rivet blank in the rivet hole While the work is clamped and holding the same between a pair of head forming anvils to locate the rivet blank axially to protrude at both sides of the work, holding one of said anvils in a fixed position relative to the rivet blank, holding said clamp members in a fixed position relative to said one anvil with a predetermined force, moving said anvils relatively toward each other against the rivet blank with a progressively increasing force whereby the end of the blank adjacent to the other anvil is squeeze-formed with the rivet blank and the work held fixed relative to said one anvil by said clamp members, and continuing said increasing force of said anvils relatively toward each other until said predetermined force on said clamp members is overcome whereby the clamp members and the work move relatively toward said one anvil and the latter forms a head at the end of the blank in abutment therewith, and continuing the relative movement of said anvils toward each other until both heads are fully formed.

8. A method according to claim 7 wherein the movement of said other anvil is substantially continuous through the head forming stages preceding and following the overcoming of the resistance of said clamp member adjacent to said one anvil.

9. A method according to claim 7 wherein said other anvil is moved against the rivet blank by a progressively increasing tluid pressure force.

10. A method according to claim 7 wherein the clamp member adjacent to said one anvil is held against the work by fiuid pressure force and wherein said other anvil is moved against the rivet blank by a progressively increasing fluid pressure force initially less than the force of said clamp member and subsequently greater than the force of said clamp member.

(References on following page) 7 References Cited UNITED STATES PATENTS Kenney 29243.53

Taylor 292435 3 Speller 29243.53X

Ross 29243.54

Colautti 227-24X Colautti 22724X l0 Havener 29526X 8 2,957,237 10/1960 Regle 29-526X 3,391,449 7/1968 Briles 29525X 1,426,473 8/1922 Harmon 22756 FOREIGN PATENTS 9,111 6/1901 Great Britain 29 243.5s

WAYNE A. MORSE, JR., Primary Examiner U.S. C1. X.R. 

